The invention relates to an arrangement in connection with a hydraulically operated impact device, such as a breaking apparatus, the impact device comprising at least a frame and a percussion piston, which is arranged to perform a reciprocating motion due to the pressure of the pressure fluid, and further means for feeding the pressure fluid into and out of the impact device, and a pressure accumulator which is connected to a pressure fluid space in the percussion piston, the accumulator being formed substantially along its entire length as an annular space surrounding the percussion piston by placing around the frame a separate sleeve comprising an annular recess, the annular space around the percussion piston being divided into two separate pressure chambers by a sleeve-like diaphragm, one of the pressure chambers being filled by a pressurized compressible medium, and the other pressure chamber being connected to a pressure fluid space of the percussion piston.
Hydraulic impact devices, such as breaking apparatuses, percussion hammers, rock drilling apparatuses and the like, are generally used to break relatively hard materials, for example stone, concrete, asphalt, frozen soil, metal slag etc. Percussion hammers are usually installed as auxiliary equipment in excavators instead of buckets, but other base machines and carriers can also be used. Thus the carrier may also be stationary. Percussion hammers are usually operated by the hydraulics of the base machine.
Hydraulic breaking apparatuses as well as other hydraulically operated machines and apparatuses employ different pressure accumulators for example to even pressure variations resulting from the cycle of operation of the machines. The pressure accumulators comprise a pressure-tight space, which is divided into at least two separate smaller spaces by means of a pressure-tight diaphragm. To the first side of the diaphragm is applied a predetermined gas pressure. The pressurized gas may be, for example, nitrogen or some other gas that is suitable for the purpose. To the second side of the diaphragm it is possible to supply pressure fluid that pushes the diaphragm forward, thus making the pressure medium provided on the first side of the diaphragm compress. However, the structure simultaneously stores energy that can be released, if required, in order to supply the pressure fluid to the desired destination. In this manner, a certain volume of pressurized fluid can be stored in the pressure accumulator. The diaphragm in the pressure accumulators is typically planar, cuplike or bladder like, and the diaphragm is placed in a spherical, cylindrical or flat frame that is separate from the rest of the actuator. In connection with impact devices, pressure accumulators are used to even out pressure variations resulting from impacts delivered by the impact piston. However, the problem with the present pressure accumulators used in impact devices is that the diaphragm thereof changes its form uncontrollably, since a momentary volume flow of the pressure fluid into or from the pressure accumulator is great and the amount of the volume flow in the pressure accumulators varies suddenly. Also, in the present pressure accumulators the material of the diaphragm is subjected to great strains and deformations, which means that the material is constantly under stress and therefore it has an unnecessarily short service life. When a diaphragm breaks, it always stops the production and creates extra costs.
In another prior art arrangement, a protruding pressure accumulator is provided at the upper end of a hydraulic percussion hammer on an extension thereof. The pressure accumulator consists of a casing that is separate from the rest of the structure, a sleeve-like diaphragm, and a metal screen placed against the inside of the diaphragm. Between the casing and the diaphragm there is a pressure space for gas, and inside the screen there is a space for pressure fluid. A disadvantage of such a structure is that when the piston has moved to its lower position, the diaphragm is pressed rapidly against the screen and may thus be damaged as it touches the openings in the screen. In time, depressions or the like may be formed in the diaphragm, whereupon the diaphragm breaks easily at these points. As in the other prior art arrangements, another problem of the aforementioned solution is that the pressure accumulator is an element which protrudes from the rest of the structure and which is thus exposed to blows and the influence of the surrounding conditions. Such a protrusion also makes the apparatus more difficult to handle. Further, a pressure accumulator provided on an extension of the percussion hammer adds to the total length of the apparatus, which is naturally disadvantageous to the use of the apparatus.